Power factor correction circuit

Abstract

A power converter that is operable to convert AC power into DC power that may be delivered to a load. The power converter operates to bypass a power factor correction (PFC) circuit during a portion of each AC power cycle. The power converter bypasses the PFC circuit when an AC input voltage is greater than a DC output voltage. The power converter may also include sensing circuitry to sense the AC input voltage and the DC output voltage of the power converter. The power converter may include one or more diodes that function to deliver power directly to a load when the AC input voltage is greater than the DC output voltage, thereby bypassing the PFC circuit. The DC output voltage of the power converter may be regulated to a level that is less than the peak AC input voltage.

1 . A power converter that is capable of receiving AC power from an AC power source on an input terminal and delivering DC power to a load on an output terminal, the power converter comprising:
 a rectifier having an input terminal coupled to the AC power source, and an output terminal, the rectifier being operable to receive an AC voltage on its input terminal and deliver a rectified voltage on its output terminal;   a power factor correction circuit having an input terminal coupled to the output terminal of the rectifier, and an output terminal coupled to the output terminal of the power converter, the power factor correction circuit being operable to modify the power factor of the power converter, and being operable to deliver DC power to a load; and   an auxiliary circuit that operates to bypass the power factor correction circuit when the magnitude of the voltage of an output terminal of the AC power source is greater than the voltage of the output terminal of the power converter.   
   
   
       2 . The power converter of  claim 1 , wherein the auxiliary circuit is operable to pass current from the AC power source to a load. 
   
   
       3 . The power converter of  claim 2 , wherein a majority of the current drawn from the AC power source passes through the auxiliary circuit during at least a portion of a cycle of the AC power source. 
   
   
       4 . The power converter of  claim 1 , wherein the auxiliary circuit operates to bypass the power factor correction circuit during at least a portion of a cycle of the AC power source. 
   
   
       5 . The power converter of  claim 1 , wherein the auxiliary circuit comprises a diode having an anode and a cathode, the anode being coupled to a node between the AC power source and the input terminal of the power factor correction circuit, and the cathode being coupled to a node between the output terminal of the power factor correction circuit and the output terminal of the power converter. 
   
   
       6 . The power converter of  claim 1 , wherein the auxiliary circuit comprises:
 a first diode, the first diode having an anode that is coupled to a first output terminal of the AC power source, and a cathode that is coupled to the output terminal of the power converter; and   a second diode, the second diode having an anode that is coupled to a second output terminal of the AC power source, and a cathode that is coupled to the output terminal of the power converter.   
   
   
       7 . The power converter of  claim 1 , wherein the power factor correction circuit is further operable to regulate the voltage at the output terminal of the power converter to a level that is less than or equal to a peak voltage of the AC power source. 
   
   
       8 . The power converter of  claim 7 , wherein the power factor correction circuit is operable to regulate the voltage at the output terminal of the power converter to a level that is approximately between 80 percent and 100 percent of the peak voltage of the AC power source. 
   
   
       9 . The power converter of  claim 1 , wherein the power factor correction circuit includes a first sensing circuit that is operable to sense the output voltage at the output terminal of the power converter, and wherein the power factor correction circuit is operable to regulate the voltage at the output terminal of the power converter dependent on the sensed output voltage. 
   
   
       10 . The power converter of  claim 9 , wherein the power factor correction circuit further includes a second sensing circuit that is operable to sense an input voltage that corresponds to the instantaneous voltage of the AC power source, and wherein the power factor correction circuit is operable to regulate the voltage at the output terminal of the power converter dependent on the sensed input voltage. 
   
   
       11 . The power converter of  claim 1 , wherein the power factor correction circuit includes an integrated circuit, the integrated circuit being operable to function at a reduced power level under predetermined conditions. 
   
   
       12 . The power converter of  claim 1 , wherein the power factor correction circuit includes:
 an inductor having a first and second terminal, the first terminal being coupled to the input terminal of the power factor correction circuit;   a diode having an anode coupled to the second terminal of the inductor, and a cathode coupled to the output terminal of the power factor correction circuit;   a controllable switch having a first terminal and a second terminal, the first terminal being coupled to a junction between the inductor and the diode, and the second terminal being coupled to ground;   a control circuit for switching the controllable switch on and off at a high frequency; and   a capacitor coupled between the cathode of the diode and ground.   
   
   
       13 . A power converter that is capable of receiving AC power from an AC power source on an input terminal and delivering DC power to a load on an output terminal, the power converter comprising:
 a rectifier having an input terminal coupled to the AC power source, and an output terminal, the rectifier being operable to receive an AC voltage on its input terminal and deliver a rectified voltage on its output terminal;   a power factor correction circuit having an input terminal and an output terminal, the input terminal being coupled to the output terminal of the rectifier, the power factor correction circuit being operable to modify the power factor of the power converter, and being operable to deliver DC power to a load;   an auxiliary circuit that operates to bypass the power factor correction circuit when the magnitude of the voltage of an output terminal of the AC power source is greater than the voltage of the output terminal of the power converter; and   a current-shaping circuit having an input terminal that is coupled to the output terminal of the power factor correction circuit, and an output terminal that is coupled to the output terminal of the power converter, wherein the current-shaping circuit is operable to reduce the harmonic distortion of an electrical current of the AC power source.   
   
   
       14 . The power converter of  claim 13 , wherein the current-shaping circuit comprises:
 a diode having an anode coupled to the output terminal of the power factor correction circuit, and a cathode coupled to the output terminal of the power converter; and   a first capacitor coupled between the cathode of the diode and ground.   
   
   
       15 . The power converter of  claim 14 , wherein the power converter further includes a second capacitor coupled between the output terminal of the power converter and ground, and wherein the first capacitor has a lower capacitance than the second capacitor. 
   
   
       16 . The power converter of  claim 13 , wherein the auxiliary circuit is operable to pass current from the AC power source to a load. 
   
   
       17 . The power converter of  claim 16 , wherein a majority of the current drawn from the AC power source passes through the auxiliary circuit during at least a portion of a cycle of the AC power source. 
   
   
       18 . The power converter of  claim 13 , wherein the auxiliary circuit comprises a diode having an anode and a cathode, the anode being coupled to a node between the AC power source and the input terminal of the power factor correction circuit, and the cathode being coupled to a node between the output terminal of the power factor correction circuit and the output terminal of the power converter. 
   
   
       19 . The power converter of  claim 13 , wherein the auxiliary circuit comprises:
 a first diode, the first diode having an anode that is coupled to a first output terminal of the AC power source, and a cathode that is coupled to the output terminal of the power converter; and   a second diode, the second diode having an anode that is coupled to a second output terminal of the AC power source, and a cathode that is coupled to the output terminal of the power converter.   
   
   
       20 . The power converter of  claim 13 , wherein the power factor correction circuit is further operable to regulate the voltage at the output terminal of the power converter to a level that is less than or equal to a peak voltage of the AC power source. 
   
   
       21 . A method for use in a power converter, the power converter being operable to receive AC power from an AC power source on an input terminal and delivering DC power to a load on an output terminal, the method comprising:
 converting an input AC voltage to a rectified voltage;   supplying the rectified voltage to a power factor correction circuit, the power factor correction circuit being operable to modify the power factor of the power converter, and being operable to deliver DC power to a load;   regulating an output voltage of the power factor correction circuit to a level that is less than a peak voltage of the AC power source; and   bypassing the power factor correction circuit when the magnitude of the voltage of an output terminal of the AC power source is greater than the voltage of the output terminal of the power converter.   
   
   
       22 . The method of  claim 21 , wherein the bypassing includes passing current from the AC power source to the load. 
   
   
       23 . The method of  claim 22 , wherein the bypassing includes passing a majority of the current drawn from the AC power source to the load during at least a portion of a cycle of the AC power source. 
   
   
       24 . The method of  claim 21 , wherein the bypassing includes passing current from the AC power source to the load through a diode. 
   
   
       25 . The method of  claim 21 , wherein the bypassing includes:
 passing current from a first output terminal of the AC power source to the load through a first diode; and   passing current from a second output terminal of the AC power source to the load through a second diode.